1. Field of the Invention
The present invention relates to a control device of a combustion apparatus for detecting an unusual state, for example, oxyzen deficient state of the combustion apparatus which warms a room by sending out a combustion gas in the room and so on.
2. Description of the Prior Art
A combustion apparatus, for example, an oil combustion apparatus, for example, for warming a room by sending out a combustion gas in the room, generally comprises an oil tank 3 and a burner 4 displaced in a space surrounded by a housing 1 and a base 2 as shown in FIG. 7. A netlike gushing part 6 is arranged at a top of the main body 5 of the burner 4 as shown in FIG. 8. Evaporated oil mixed beforehand with an air gushes from the net of the gushing part 6 and is ignited by a spark emitted from a ignition electrode 7 to the net of the gushing part 6, and the evaporated oil burns. As shown in FIG. 7, the combustion gas A of the burner 4 is mixed with an air B draughted from the room to be heated by a fan 9 driven with a motor 8. The mixed warm gas C is sent out through a louver 10 and warms the room.
It is feared that an oxygen deficiency accident occurs when such combustion apparatus which consumes oxygen in the room for the combustion is used for a long time with the room being shut tightly. Then such combustion apparatus has a flame rod 12 disposed in a flame 11 of the burner 4, for detecting oxygen deficient state. That is, when the oxygen deficiency occurred the flame 11 becomes extremely unstable and a flame rod current which flows between the flame rod 12 and the burner 4 through the flame 11 decreases. Therefore, when the flame rod current decreases less than a predetermined value, it is judged that the oxygen deficient state occurs, and the combustion in the combustion apparatus is automatically stopped. A conventional control device for executing the above-mentioned operation is disclosed in FIG. 9.
An alternating current power source 13, point a, a first relay contact 14, a burner heater 15, point b and a driving switch 16 together form a closed loop circuit. A second relay contact 17 and a parallel circuit of a fan motor 5 and a burner motor 18 are connected between the point a and the point b as shown in FIG. 9. Further, a third relay contact 19, point c and an oil pump 20 are connected between the point a and the point b. A high tension ignition device 21 is connected between point c and point b as shown in FIG. 9. A control circuit 22 including a relay control circuit and a safety device control circuit is connected between point a and point b.
Further, a DC constant voltage power source 23, point d, a resistance 24, point e, a resistance 25 and point f together form a closed loop circuit. An AC power source 26, a protection resistance 27, point g, a parallel circuit of a resistance 28, a capacitor 29, point f, the flame rod 12 and the burner 4 together form a closed loop circuit. The voltage at point g is supplied to a plus input terminal of an operational amplifier 30 for detecting an oxygen deficiency. The voltage at point e is supplied as a reference voltage to a minus input terminal of the operational amplifier 30. An output signal of the operational amplifier 30 is supplied to the control circuit 22.
The operation of the conventional control device in FIG. 9 is as follows. When the driving switch 16 is closed, the first, second and third relays 14, 17 and 19 are closed by the control circuit 22 and the heater 15 heats a carburetor in the burner 4, thereby to maintain the carburetor at a constant temperature. Accordingly, an oil sent into the carburetor by the oil pump 20 is evaporated and is mixed with an air sent in by the burner motor 18. The mixed evaporated oil gushes out from the netlike gushing part 6. The ignition device 21 makes a spark between the ignition electrode 10 and the netlike gushing part 6, thereby to ignite the evaporated oil. A flame rod current flows through the flame of the ignited oil between the flame rod 12 and the burner 4. As a result, a voltage is impressed to the parallel circuit of the resistance 28 and the capacitor 29. Incidentally, the circuit of the flame rod 12, the flame and the burner 4 has a function of rectification. The voltage at point g is supplied to the plus input terminal of the operational amplifier 30.
On the other hand, a constant voltage at point e, determined by dividing the voltage of the DC constant voltage power source 23 with the resistances 24 and 25, is supplied to the minus input terminal of the operational amplifier 30.
Then, the flame rod current changes according to the various combustion state, therefore the voltage at point g also changes. The variation is described by using FIG. 10. The voltage E.sub.0 at point e is normally constant as apparent from the above-mentioned matter. On the contrary, the voltage at point g varies. That is, the voltage at point g is 0 when the combustion apparatus does not burn. When the combustion apparatus burns, after a predetermined time from the ignition, the voltage at point g increases and becomes a voltage G.sub.1 which is larger than the voltage E.sub.0 at point e. Therefore, the operational amplifier 30 does not issue an oxygen deficient signal to the control circuit 22.
Incidentally, the operational amplifier 30 operates only after the predetermined time from the ignition, by utilizing a timer. Therefore, an erroneous operation of the operational amplifier 30 at a starting time of the combustion apparatus can be prevented.
When an oxygen deficiency occurs the flame rod current decreases and the voltage at point g decreases largely to a voltage G.sub.3 and becomes less than the voltage E.sub.0 at point e. Accordingly, the operational amplifier 30 issues an oxygen deficiency signal to the control circuit 22.
Then, as above-mentioned, the conventional control device of the combustion apparatus can operate normally so far as an atmosphere temperature is normal.
In case, when the atmosphere temperature is low, for example, at 0.degree. C. to -20.degree. C., the density of the air increases, but the oil supply amount does not increases for the raise of the density of the air. As a result, the air becomes oversupplied and the flame transfers upwards, thereby the flame rod current decreases. Therefore, the voltage at point g becomes voltage G.sub.2 which is lower than voltage E.sub.0 as shown by a chain line g' in FIG. 10. Then, the operational amplifier 30 issues an unusual signal and the combustion of the combustion apparatus is stopped, even though the oxygen deficiency does not occurs. As mentioned above, the conventional control device of the combustion apparatus has a disadvantage.